Multiple simultaneous browser sessions

I'm looking for a chrome or firefox plugin that allows me to have windows with different sessions. It's a bit like chrome's incognito works: if you open an incognito window, it won't share the cookies with the "normal" browser window.

I'm searching for a solution that allows me to create several windows (incognito only allows two: the main window and the incognito window), each with a different session (i.e., without sharing cookies between browser windows).

Any thoughts? I'm using OSX.

Chrome has this functionality baked in: http://www.chromium.org/user-experience/multi-profiles

If you hit settings (command-, on OSX), you'll see a "Users" section. Simply add users to generate multiple profiles within Chrome, each of which containing its own cookie jar, history, etc.

Not tested, but I think you could do this by using different configuration directories. I don't know about OSX but on linux you can copy .config/google-chrome/ and create .config/google-chrome1/, .config/google-chrome2/, .config/google-chrome3/, etc. You can start each separate browser with google-chrome --user-data-dir=.config/google-chrome1/.